Sodium hydrosulfite stabilization composition

ABSTRACT

The present discovery entails a new means for stabilizing mixtures, containing primarily sodium dithionite, from spontaneous decomposition and &#39;&#39;&#39;&#39;ignition&#39;&#39;&#39;&#39; by the action of water. Specifically, the invention comprises stabilization of sodium hydrosulfite against spontaneous decomposition in the presence of water, using effective quantities of additives, which still in no way lessen the bleaching activity that would be developed by an equivalent quantity of sodium hydrosulfite. The stabilizing agents consist of oxalic acid and a water soluble inorganic carbonate. This mixture can be further improved as to stabilization and bleaching effect by the addition of borax (Na2B4O7 1 10 H2 O). The bleaching effect may be improved by adding a water soluble inorganic sulfite.

United States Patent Shastri 1 June 13, 1972 SODIUM HYDROSULFITE STABILIZATION COMPOSITION Inventor:

US. Cl ..252/188, 8/107, 23/116,

252/105 Int. Cl. ..C0lb 17/98, D2 lc 9/10 Field oISearch .252/188, 105; 23/1 16; 8/107 References Cited UNITED STATES PATENTS Primary Examiner-Leon D. Rosdoi Assistant Examinerlrwin Gluck Attorney-J. Gibson Sernmes 57] ABSTRACT The present discovery entails a new means for stabilizing mixtures, containing primarily sodium dithionite, from spontaneous decomposition and "ignition" by the action of water. Specifically, the invention comprises stabilization of sodium hydrosulfite against spontaneous decomposition in the presence of water, using effective quantities of additives. which still in no way lessen the bleaching activity that would be developed by an equivalent quantity of sodium hydrosulfite. The stabilizing agents consist of oxalic acid and a water soluble inorganic carbonate. This mixture can be further improved as to stabilization and bleaching efi'ect by the addition of borax (Na B O 10 H 0). The bleaching effect may be improved by adding a water soluble inorganic sulfite.

l1 Claim, No Drawings SODIUM HYDROSULFITE STABILIZATION COMPOSITION BACKGROUND OF THE INVENTION Sodium hydrosulfite, also designated as sodium dithionite, is used in large quantities as a strong reducing medium for bleaching and the reduction of certain dyes for example groundwood pulp bleaching and vat dye reductions. Although it fulfills these purposes satisfactorily, the application of sodium hydrosulfite in these areas is deterred because of self-ignition in contact with small quantities of water leading to the rapid expansion of the decomposition, which interferes with efi'icient pulp bleaching, etc. and hinders the papermill operation in particular.

In the reaction initiated by water, a series of strongly exothermic reactions develop apparently yielding hydrogen and several sulfur-containing compounds of various oxidation states of sulfur. Small amounts of water, for example, from a drum of moist sodium dithionite, mixed with dry product in a storage bin or hopper can start a severe decomposition in the absence of significant amounts of oxygen, which, upon aeration and evolution of gases can lead to intense combustion and possibly explosion.

Various attempts have been made to reduce the sensitivity of sodium hydrosulfite to moisture by the use of additivies of various kinds, e.g., by the addition of dessicants of various compositions or through the wetting of the sodium dithionite with hydrophobic compounds. Although these additives have been partially successful, their additions generally diminish the bleaching efficiency of the product, at least in proportion to their presence.

The use with sodium hydrosulfite is therefore carried out in paper mill operations with increasing care and concern because ofthe generally humid conditions and the presence of large quantities of water in paper processing; these problems have discouraged the use of sodium dithionite in the industry.

For this reason, zinc hydrosulfite, (zinc dithionite), ZnS O is preferred as a bleaching agent, since it is relatively stable toward spontaneous self-decomposition under normal transport and storage conditions. However, the zinc ion is considered toxic, therefore its presence in effluents from mills is not tolerated in many instances. Therefore, the user has a choice, between sodium hydrosulfite with its undesirable decomposition characteristics and zinc hydrosulfite with its toxic characteristics, necessitating the use of prohibitively expensive removal processes for the treatment ofeffluent waters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The term sodium hydrosulfite (dithionite) refers herein to the article of commerce which may contain between 85 and 98 percent weight percent sodium hydrosulfite (dithionite) along with certain impurities such as sodium chloride, sodium sulfate, sodium sulfite and thiosulfate.

Exemplary of the water soluble inorganic carbonate are the alkali metal carbonates and bicarbonates and ammonium carbonate. The sodium salts are preferred for economic reasons. For example: a mixture of approximately equal parts of sodium carbonate and sodium bicarbonate has been found to be satisfactory.

Exemplary of water soluble inorganic sulfites are the alkali metal and ammonium sulfites and bisulfites, the sodium salt being preferred. A mixture of additives consisting of approximately equal amounts of sodium sulfite and bisulfite is preferred.

With the exception of borax, it is desirable in the practice of this invention to use these ingredients in their anhydrous state. The presence of the water of crystallization in the borax has no adverse effect upon the application of this composition.

In practice hereunder, the desirable ranges of use of ingredients, based upon the weight of technical sodium hydrosulfite employed, are as follows:

a. oxalic: l to-25 percent b. carbonate: l to-3 percent c. borax: l to-5 percent d. sulfite: 0.5 to-l percent.

For practical purposes, the sum total ingredients aforesaid should not exceed 25 weight percent of the technical hydrosulfite content.

By the use of this mixture herein the generation of heat due to effect of moisture develops more slowly so that the critical temperature for spontaneous decomposition is not reached.

The composition of matter mixtures herein are compatible with the normal bleaching adjuvants such as are used in the bleaching of pulp particularly for example the complexforrning ingredients such as the polyphosphates and the various derivatives of ethylene diamine tetraacetic acid and nitrilo-triacetic acid. The adjuvants can be used herein by separate addition or as components of proprietary mixtures.

EXAMPLE I In a specific experiment designed to demonstrate the stabilization of sodium hydrosulfite against spontaneous decomposition caused by moisture the following formulation of comparable bleaching efficiency proved successful.

To 180 grams of commercial grade of sodium hydrosulfite the following components were added. The amount of additives comprised a total of 20 grams:

10 grams oxalic acid, anhydrous 6 grams of a carbonate comprising sodium bicarbonate and sodium carbonate in equal quantities 2 grams borax; and

2 grams of sulfites, containing respectively equal portions of sodium metabisulfite and sodium sulfite Commercial grade sodium hydrosulfite was placed in a stoppered bottle fitted with a gas evolution tube extending substantially through the stopper and with a second tube extending through the stopper to the bottom of the bottle. When 3 percent water was added through the bottom-extending tube, heat was evolved and the gas liberated was ignited when a bunsen flame was applied.

The composition of matter mixture described was thereafter applied to a hydrosulfite and the same amount of water added. This produced a comparatively lower reaction temperature and the decomposition products liberated could not be ignited with the bunsen flame.

EXAMPLE II The following composition was used to demonstrate improved sodium hydrosulfite stability and particularly improved bleaching efficiency.

l. percent sodium hydrosulfite 2. 2 percent sodium sulfite 3. 10 percent oxalic acid 4. 3 percent sodium borate 5. 5 percent sodium tripolyphosphate In an actual bleaching experiment, the product undergoing examination being spruce stone groundwood, the results below were obtained under these conditions.

A 3 percent consistency pulp slurry of the groundwood was treated for 45 minutes at F. at a pH of 5.0 to 5.5, the treatment being at a rate of IO lbs of hydrosulfite composition per ton of air dried groundwood pulp, aforesaid. The results are listed below.

(l) Brightnesses were measured on the Elrepho Electric Photo-Reflectometer using a magnesium oxide standard as l00%brightness.

I claim:

1. A stabilized composition of matter consisting essentially of a predetermined percent by weight of sodium hydrosulfite characterized by additives of oxalic acid and a water soluble inorganic carbonate, the percentages of weight of additives, relative to the sodium hydrosulfite, being not less than 1 percent nor more than 25 percent, said additives stabilizing the sodium hydrosulfite against spontaneous thermal decomposition.

2. The composition of matter of claim 1, and borax as a further additive.

3. The composition of matter of claim 2, and a water soluble inorganic sulfite as further additive.

4. The composition of matter of claim 1 wherein the inorganic carbonate is selected from the group consisting of sodiurn hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.

5. The composition of matter of claim 2 wherein the inorganic carbonate is selected from the group consisting of sodium hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.

6. The composition of matter of claim 3 wherein the inorganic carbonate is selected from the group consisting of sodium hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.

7. The composition of matter of claim 3 in which the water soluble inorganic sulfite is selected from the group consisting of sodium sulfite and sodium bisullite and mixtures thereof.

8. The composition of matter of claim 4 in which the water soluble inorganic sulfite is selected from the group consisting of sodium sulfite and sodium bisulfite and mixtures thereof.

9. The composition of matter of claim 1 wherein the propor tion of additives in percentage by weight to sodium hydrosulfite is:

A. oxalic acid 1-25 percent;

B. carbonate 1-3 percent.

10. The composition of matter of claim 9 wherein a further additive, borax, comprises in proportion by weight relative to the sodium hydrosulfite, 1-5 percent.

11. The composition of matter of claim 9 wherein a further additive of sulfites comprises in proportion by weight relative to the hydrosulfite 0.5-l percent.

* i i II 

2. The composition of matter of claim 1, and borax as a further additive.
 3. The composition of matter of claim 2, and a water soluble inorganic sulfite as further additive.
 4. The composition of matter of claim 1 wherein the inorganic carbonate is selected from the group consisting of sodium hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.
 5. The composition of matter of claim 2 wherein the inorganic carbonate is selected from the group consisting of sodium hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.
 6. The composition of matter of claim 3 wherein the inorganic carbonate is selected from the group consisting of sodium hydrogen carbonate and mixtures thereof and sodium carbonate as water soluble inorganic carbonates.
 7. The composition of matter of claim 3 in which the water soluble inorganic sulfite is selected from the group consisting of sodium sulfite and sodium bisulfite and mixtures thereof.
 8. The composition of matter of claim 4 in which the water soluble inorganic sulfite is selected from the group consisting of sodium sulfite and sodium bisulfite and mixtures thereof.
 9. The composition of matter of claim 1 wherein the proportion of additives in percentage by weight to sodium hydrosulfite is: A. oxalic acid 1-25 percent; B. carbonate 1-3 percent.
 10. The composition of matter of claim 9 wherein a further additive, borax, comprises in proportion by weight relative to the sodium hydrosulfite, 1-5 percent.
 11. The composition of matter of claim 9 wherein a further additive of sulfites comprises in proportion by weight relative to the hydrosulfite 0.5-1 percent. 